This application claims the priority of German patent document 101 01 991.2, filed Jan. 18, 2001, the disclosure(s) of which is (are) expressly incorporated by reference herein.
This invention relates to a method of signal treatment and processing in a rotating synthetic aperture radar (ROSAR) system.
German patent documents DE 39 22 086 and DE 43 23 511 disclose a ROSAR system that operates on-line in near real time, and can be used not only in mapping, obstacle warning, and mine detection applications, but also for target reconnaissance and tracking, and for missile guidance. This ROSAR device is used at pulse frequency or in FM-CW operation, and operates in the cm- or in the mm-wavelength range. The present invention builds upon this state of the art.
In its operation, ROSAR is a side-looking radar, and thus supplies no elevation data. Up to now, a ROSAR has been implemented under the concept of xe2x80x9cheliradarxe2x80x9d, using a turnstile that is specially designed for this purpose and is mounted on the rotor shaft of the helicopter. In order to obtain xe2x80x9croughxe2x80x9d elevation data, transmitting and receiving antennas having low vertical dimensions have been provided on the turnstile, in order to achieve at least a compromise or tradeoff between a loss of aerodynamic flight performance and elevation angle resolution. While the degradation of flight performance caused by the turnstile is significant, experts have considered it tolerable in view of the all-weather vision that is gained.
The rough elevation resolution obtained in this manner is achieved by the radiation pattern of the transmitting and receiving antennas, which are fanned out to elevation angles. Because the elevation angle resolution that is achieved is related to the reciprocal of the antenna dimension (in this case, vertical), xe2x80x9cvertical projectionsxe2x80x9d at the tip of the turnstile (that tend to reduce flight performance) must be tolerated. In addition, there is the problem created by the need to transmit a large amount of electrical power from the fixed airframe of the helicopter to the rotating capstan handle.
As indicated above, known ROSAR signal treatment and processing methods obtain elevation data about the surrounding area to be imaged via vertically fanned transmitting and receiving antennas that are integrated into the ends of a turnstile. The turnstile rotates synchronously with the helicopter rotors. However, the integration of the vertically divided fanned transmitting and receiving antennas results in the above-mentioned vertical projections, which in turn result in the discussed reduction in flight performance. Added to this is the fact that a complicated rotary coupling is necessary to transmit the high-frequency transmitting energy from the helicopter airframe to the turnstile.
One object of the present invention is to provide a ROSAR method that will largely diminish the above-mentioned disadvantages of the current state of the art.
Another object of the invention is to provide such a method which will ensure high elevation resolution.
These and other objects and advantages are achieved by the method of signal conditioning and processing according to the invention, which achieves high resolution elevation data using a fixed transmitting antenna. For this purpose, a telescope-like extensible transmitting antenna having large vertical dimensions illuminates the area to be imaged in a fanned pattern, creating overlapping elevation sectors.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.